196 Transactions of the American Institute. 



cacy of the apparatus is so greatly exalted as to render it unfit for a 

 locality like the present. I slightly lower the note of the first fork 

 by loading it with a nickel cent, attaching it with wax, and observe 

 that the second fork, with the mirror, now pays no attention to its call ; 

 the spot of light remains stationary. 



Let us make an application of our experiment. In the ear, in the 

 strangely shaped cavity, we find a multitude of very small elastic 

 rods, fastened at one end just like our tuning-fork, and, like it, capa- 

 ble of vibrating only when the particular notes to which they are 

 tuned are struck. When this happens to one of these rods, it is set 

 in vibration, and affects the delicate nerve fibril connected with it, 

 and we have the sensation due to a particular rate of vibration, due 

 to a particular note. A drawing of some of these rods, enormously 

 magnified, is on the screen. But, for the full illustration of this mat- 

 ter, I need yet one more experiment, and must ask you to make it for 

 me when you go home this evening. Open a piano, and, while press- 

 ing with the foot on the right-hand pedal, pronounce in a clear loud 

 voice over the strings, for example, the vowel sounds, and you will 

 find that the strings, which are capable of giving the notes of which 

 they are built up, will be set in vibration, and will echo back to you, 

 in a far-off, ghostly way, the sound you have just uttered. So, in all 

 probability, is it in the ear; for we find there, locked up in its bones, 

 in the strangely shaped cavity, an instrument with not less than 3,000 

 strings, tuned, as we believe, to different notes, and connected with 

 different nerve filaments, ready to transmit to the brain the sensations 

 due to different notes. A drawing of a portion of this wonderful 

 contrivance, which has been particularly described by the Marchese 

 Corti, is on the screen, and some of the strings can be seen. Its pro- 

 bable action is as follows : When a sound composed of a number of 

 notes reaches it, the compound tone is analyzed into its constituents, 

 the corresponding cords vibrate as in the piano experiment, and, by 

 their action on the nerves, reproduce the appropriate sensations. 



The two contrivances I have described are well fitted to make us 

 sensible of sounds which are sufficiently prolonged to allow of the 

 reception of a certain number of vibrations by the sympathetic appa- 

 ratus in the ear ; but in those cases where the vibrations, though pow- 

 erful, are very few in number, it is probable that the cords and rods 

 would fail to take cognizance of them, that is, they are probably deaf 

 to short, quick sounds, generated by a single blow or impulse, and yet 

 it is just these sounds which often announce the presence of danger. 

 This case has also been provided for, curiously enough, by introducing 



